A large proportion (some estimates are as high as twenty-five percent) of the electricity generated in the United States each year goes to lighting. Accordingly, there is an ongoing need to provide lighting which is more energy-efficient.
One type of conventional light is referred to as a back-reflecting lamp. With such a light, a light source (or plural light sources) is oriented so as to emit light toward a reflector, such that light that is emitted by the light source is reflected by the reflector and exits the light in a direction generally opposite to the direction that it is emitted by the light source. Well known examples of such back-reflecting lamps include most PAR lamps and most MR lamps.
PAR lamps are widely used for concerts, nightclubs and touring productions. PAR cans come in a variety of sizes and shapes; from the small PAR16 to the 1000 watt PAR64.
“PAR” is an acronym for parabolic aluminized reflector and is used to designate a sealed-beam lamp similar to the headlight in an automobile. PAR lamps are available in an assortment of wattages and beam spreads as well. For example, a PAR56 lamp may be purchase at 300 or 500 watts, and each wattage is available in Narrow Spot, Medium Flood or Wide Flood.
Typically, a PAR can is a lamp housing that safely holds the lamp and any color media (gel) in place. The can may also have a mounting bracket that allows it to be bolted to a light bar or truss or by use of a pipe clamp.
“MR” stands for multifaceted reflector, a pressed glass reflector with the inside (reflecting side) surface composed of facets and covered by a reflective coating. These facets provide optical control by gathering the light from the filament to create a concentrated beam of light. The reflectors of some MR lamps have a smooth inside surface instead of facets, but they are still called MR lamps by convention.
The light source of MR lamps is usually a single-ended quartz halogen filament capsule. The reflective coating of MR16 lamps is usually either dichroic or aluminum. A dichroic coating is a thin, multi-layer dielectric (non-metallic film) that allows infrared radiation (heat) from the filament capsule to pass through the reflector while it reflects visible radiation (light) forward. An aluminum coating is a thin film of aluminum that, unlike the dichroic coating, reflects both infrared and visible radiation. Some MR16 lamps have a cover glass on the front end of the reflector. This cover is a safety measure designed to contain any broken fragments in case the lamp shatters when it fails.
FIGS. 1 and 2 depict a conventional back-reflecting PAR lamp (or “reflector lamp”). FIG. 1 is a top view, and FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1. FIGS. 1 and 2 show a lamp 10 that comprises a light source 11 and a reflector 12. The light source 11 is aimed at the reflector 12 such that light from the light source 11 is directed away from the aperture 13 of the reflector 12 and then is reflected by the reflector 12 out the aperture 13 of the reflector 12. The light source 11 is suspended on a bridge 14 that extends diametrically across the aperture 13 (alternatively, the bridge 14 can cantilever radially over the aperture 13).